1. Field of the Invention
The present invention is related to a method capable of improving image quality and the related color compensating device and image processing device, and more particularly, to a method which can reduce the color flickering phenomena in a television system and the related color compensating device and image processing device.
2. Description of the Prior Art
NTSC, PAL and SECAM are the three most popular analog television systems. Among them, the SECAM system was first developed by some research groups in France and former Soviet Union, and was adopted in numerous countries, like France, countries of former Republics of Soviet Union and some other countries which are former French colonies. The word SECAM is abbreviated from “Séquentiel couleur à mémoire” in French language, and can be translated as “Sequential Color with Memory.” While in the development stage of the SECAM system, the researchers noticed that the bit rate of the chrominance components of the image signal is less than the bit rate of the luminance component; therefore, the SECAM system developers assigned a larger bandwidth for the luminance signal Y, and a relatively smaller bandwidth for the chrominance components Cb and Cr. Meanwhile, for further squeezing the bandwidth of the chrominance (color) components, the chrominance components Cb and Cr of the SECAM system are being sent to the receiving end by turns, and only one of the chrominance components Cb and Cr is being sent for every pixel. In other words, for every horizontal raster line of the SECAM system, only Cb or Cr is being sent. Therefore, the receiving end of the SECAM signal should first recover the “lost” Cb or Cr which was unsent intentionally by the transmitter, such that a picture can be displayed normally. Please refer to FIG. 1A, which illustrates the distribution of the chrominance components of two reciprocal fields Field(k) and Field(k+1) in a typical SECAM TV picture. Inside FIG. 1A, the symbols Line(n)˜Line(n+11) denote raster lines in a frame or in a number of frames, and it can be observed that for every raster line in a frame, only one of the two chrominance components Cb or Cr is being sent, and the chrominance component Cb or Cr is presented in an alternative fashion in a field signal.
Since the SECAM system transfers its TV signals according to an interlaced format, a complete frame should compose of an odd and an even field, and was then transmitted in odd and even fields. Also, in a traditional SECAM TV, the pictures displayed on the screen are also switching between odd fields and even fields for filling the screen. Please refer to FIG. 1B, which illustrates a schematic diagram of the chrominance components Cb and Cr of a column of data of a SECAM TV screen picture displayed as time evolves. The symbol Field(k) denotes the chrominance data of a specific column of the k-th field in temporal domain, and Field(k+1) denotes the chrominance data of the same column of the (k+1)-th field in time, and so forth. Noticeably, any raster line in a field is interlaced with the raster line of its neighboring field(s). Besides, the SECAM TV signal contains 25 frames of picture per second, or 50 fields of picture per second, and hence the time interval between any two neighboring fields is approximately 0.02 seconds.
Briefly speaking, a single field of picture in a SECAM TV signal is insufficient for forming a complete picture, and any field (odd or even) must be combined with its reciprocal field to become a complete picture. In the recent years, a new generation of TV sets using progressive scan has become more popular. The new TV set using the progressive scan displays the picture by frames instead of fields. For a TV set using progressive scan to display a traditional SECAM TV signal using interlaced format, the picture format of the traditional SECAM TV signal must be transformed into frames. In other words, for a progressive scan TV set to display a SECAM signal, the unsent parts of the chrominance signals Cb or Cr must first be “compensated” for a complete field signal, and then the field signal (still the interlaced format) must be compensated to become a frame signals to fit the TV set in progressive format.
Please refer to FIG. 2, which illustrates a schematic diagram of a TV signal decoder 20 of a SECAM TV system of the prior art. The TV signal decoder 20 comprises an analog-to-digital converter 200, an image decoder 204 and a deinterlacer 206. Generally speaking, the analog-to-digital converter 200 converts an analog signal Acol into a digital signal Dcol in 8- to 10-bit format. The image decoder 204 outputs a chrominance component indicator SECAM_cb and an interlaced chrominance signal INTLC0 according to the digital signal Dcol. Please refer to FIG. 3A, which illustrates a schematic diagram of the chrominance components Cb and Cr of the SECAM TV signal in both the temporal and the spatial domain, and is used to represent the output result of the image decoder 204. Inside FIG. 3A, the original chrominance signals are represented by the symbols Cb0 and Cr0, and the parameters inside the parenthesis represent the line number of the raster lines shown. In brief, the image decoder 204 not only needs to decode the original chrominance signals Cb0 and Cr0, but also needs to estimate the primary chrominance components which are not presented in the digital signal Dcol. For example, Cb0(n+1) represents the original chrominance signal Cb0 in the (n+1)-th raster line, which is decoded directly from the digital signal Dcol, and the primary compensating chrominance signals, which are estimated by the image decoder 204, are denoted as Cbp and Crp. Inside FIG. 3A, the primary chrominance signals Cbp and Crp are underlined to differentiate further from the original chrominance signals Cb0 and Cr0. Meanwhile, The arrow signs shown in FIG. 3A demonstrate how the image decoder 204 estimates the primary compensating chrominance signals; that is, the primary compensating chrominance signals Cbp and Crp are simply derived from the original chrominance components Cb0 and Cr0 from the previous raster line in the same field. Besides that, a color component indicator SECAM_cb is utilized for indicating the original chrominance component of the current raster line is a Cb or a Cr; when SECAM_cb=1, it represents the current chrominance component Cb is an original chrominance signal Cb0, and the current chrominance signal Cr is a primary compensating chrominance signal Crp; on the other hand, if SECAM_cb=0, it represents the current chrominance component Cb is a primary compensating chrominance signal Cbp, and the current chrominance signal Cr is an original chrominance signal Cr0. Next, the deinterlacer 206 is used to estimate the chrominance signal INTLC1 which is reciprocal to the chrominance signal INTLC0 in a complete frame picture. Please refer to FIG. 3B, which illustrates the distribution of the chrominance components after the deinterlacer 206 has generated the reciprocal chrominance signal INTLC1. According to FIG. 3B, the chrominance signals INTLC0 and INTLC1 interlace each other to form a complete frame picture. By taking the frame signal Frame(k) as an example, the chrominance signal INTLC0 is equivalent to the field signal Field(k), and the chrominance signal INTLC1 is reciprocal to the chrominance signal INTLC0, which includes the chrominance components in the raster lines Line(n), Line(n+2), Line(n+4) . . . etc. Or, by taking the frame signal Frame(k+1) as an example, the chrominance signal INTLC1 will contain the chrominance components in the raster lines Line(n+1), Line(n+3), Line(n+5) . . . etc. As depicted in FIG. 3B, the secondary compensating chrominance signals Cbs and Crs, which are contained in the chrominance signals INTLC1, belong to the same field. Besides, the chrominance signals INTLC0 and INTLC1 of the same field are reciprocal to each other, and the chrominance signal INTLC0 contains the original chrominance signals Cbp and Crp, and the primary compensating chrominance signals Cbp and Crp.
Noteworthily, the deinterlacer 206 uses a 2D (two-dimensional) deinterlace algorithm or a 3D (three-dimensional) deinterlace algorithm to generate chrominance signal INTLC1. Firstly, please refer to FIG. 3C, which illustrates the distribution of the chrominance components after the deinterlacer 206 has compensated the reciprocal chrominance signal INTLC1 by using the 2D algorithm. The 2D algorithm used by the deinterlacer 206 is to calculate every pixel's secondary compensating chrominance signal Cbs and Crs in the chrominance signal INTLC1 by taking the average of the chrominance components Cb0, Cr0, Cbp and Crp of the neighboring pixels (from above and below) in its reciprocal chrominance signal INTLC0. Next, please refer to FIG. 3D, which illustrates the distribution of the chrominance components after the deinterlacer 206 has compensated the reciprocal chrominance signal INTLC1 by using the 3D algorithm. The 3D algorithm used by the deinterlacer 206 is to calculate every pixel's secondary compensating chrominance signals Cbs and Crs by taking the average of the pixels' chrominance components Cb0, Cr0, Cbp and Crp from the chrominance signals INTLC0 of the previous and the following pictures. Also, please note that the secondary compensating chrominance signals in FIG. 3B are denoted as Cbs and Crs, and for better demonstrating the methods used in the 2D and 3D deinterlace process, FIG. 3C and 3D have used the math formula in terms of the chrominance components Cb0, Cr0, Cbp and Crp instead to demonstrate the process of color compensation of the 2D and the 3D deinterlace process.
Simply speaking, after the SECAM TV signals have been processed by the TV signal decoder 20, which includes the analog-to-digital converter 200, the image decoder 204 and the deinterlacer 206, the output becomes a series of frame pictures, and can be directed to the progressive TV for display. However, by investigating the operation of the TV signal decoder 20, a strange phenomena about picture quality can be observed in the chrominance signal INTLC0 output by the image decoder 204. Please refer to FIG. 4A, which illustrates a distribution of the original chrominance signals Cb0, Cr0. There exists two different colors in FIG. 4A, and the chrominance components of the two colors are represented as Cb1, Cr1 and Cb2, Cr2, respectively. Between the raster lines Line(n+5) and Line(n+6), there is an imaginary horizontal boundary between the two colors. Please refer to FIG. 4B, which illustrates a distribution of the original chrominance signals Cb0, Cr0 and the primary compensating chrominance signal Cbp, Crp. According to the operating principles of the image decoder 204 and as shown in FIGS. 4A and 4B, the primary compensating chrominance signals Cbp, Crp of Line(n+6) are directly copied from the original chrominance signals Cb0, Cr0, of Line(n+4), and also, the primary compensating chrominance signals Cbp, Crp of Line(n+7) are directly copied from the original chrominance signals Cb0, Cr0 of Line(n+5). Then, when the TV set plays the picture as specified in FIGS. 4A and 4B, it can be observed that the raster line Line(n+6) of the field signals Field(k−1) and Field(k+1) will have its chrominance signals switched from Cb2, Cr1 to Cb1, Cr2, and then back to Cb2, Cr1 in Field(k+3) (not shown in the figure); on the other hand, the raster line Line(n+7) of the field signals Field(k) and Field(k+2) will have its chrominance signals switch from Cb1, Cr2 to Cb2, Cr1, and then back to Cb1, Cr2 in Field(k+4) (not shown in the figure). And, as long as the picture keeps playing at the speed of about 50 fields per second, the color switching (flickering) phenomena will not stop. In other words, the color signals in raster lines Line(n+6) and Line(n+7) will exhibit an unstable phenomena where the color pixels in the color boundary keep flickering. Similarly, when TV displays slow-moving or still color movies, pixels on the color boundary are very likely to display the same unfavorable phenomena of color flickering. Furthermore, since the deinterlacer 206 is to generate the reciprocal color signals INTLC1 according to the input color signal INTLC0, the area of the color flickering in the color signal INTLC0 can be expanded further by the deinterlacer 206 such that an ordinary user can see it easily.